[R] Palette color order in bwplot (lattice violin plot) vs. boxplot

[Deepayan Sarkar]

On Thu, Apr 1, 2010 at 4:10 AM, Luigi Ponti <lponti at inbox.com> wrote:
> Hello,
>
> I am trying to give different colors to boxes in a violin plot obtained via
> bwplot from lattice package using a color palette from RColorBrewer:
>
>> require(RColorBrewer)
>> MyPalette <- brewer.pal(6, "Set3")
>
> A call to:
>
>> boxplot(count ~ spray, data = InsectSprays, col = MyPalette)
>
> yields the example boxplot with each box colored according to the different
> colors from MyPalette. In addition, boxes are colored with the same color
> order of MyPalette. See
>
>> display.brewer.pal(6, "Set3")
>
> However, when I do the same thing with a violin plot from the lattice
> package
>> require(lattice)
>> bwplot(count ~ spray, data = InsectSprays,
> +        panel = function(..., box.ratio) {
> +            panel.violin(..., col = "transparent",
> +                         varwidth = FALSE, box.ratio = box.ratio)
> +            panel.bwplot(..., fill = MyPalette, box.ratio = .1)
> +        } )
>
> boxplots are colored with the right colors (each box has a different color)
> but with a different color order -- too bad because I would like to color
> code the plot according to certain pre-defined colors. Same thing (wrong
> color order) with a simple bwplot:
>
>> bwplot(count ~ spray, data = InsectSprays, fill = MyPalette)
>
> Is there a way to get the right color (i.e. same order as in MyPalette) in
> bwplot/panel.violin?

The correct approach would be along the lines of

bwplot(count ~ spray, data = InsectSprays,
       groups = spray,
       panel = panel.superpose,
       panel.groups = panel.violin,
       col = MyPalette)

(unlike panel.xyplot etc., panel.bwplot does not explicitly handle grouping).

-Deepayan